Partial discharges (PD) diagnostics play an important role in insulation diagnosis of HV power cables all over the world. By application of such diagnostic it is possible to asses the quality of final product (cable) during factory test, during after-laying test or during service life. In this way knowledge about the discharging defects in a particular cable insulation system including the accessories can be done. Using sensitive PD diagnostic parameters like: PD inception voltage, PD magnitude, PD fingerprint pattern characteristics, can help to recognize the symptoms of discharging insulation weak spots. In this contribution the application of two different PD detection methods will be discussed: conventional PD detection according to IEC 60270 and unconventional radio frequency (RF) PD detection. To investigate the sensitivity issues both methods have been applied to full size 150 kV cables system (length of 100 m). An example of insulation defect in a cable joint was used to investigate above mentioned PD detections methods as applied at different types of AC voltage energizing: continuous AC and damped AC voltages. Observed PD parameters have been analyzed and compared for both energizing methods (AC 50 Hz and DAC 60 Hz and 400 Hz) and PD detection methods.@en